Defrostable refrigeration system



March 19, 1963 c. J. REBER, JR

DEFROSTABLE REFRIGERATION sys'rm Filed Oct. 22, 1959 INVENTOR. memo .z Mam, m.

W M. l Wm United States Patent 3,081,607 DEFROSTABLE REFRIGERATION SYSTEM Carroll J. Reber, Jr., Havertown, Pa., assignor, by mesne assignments, to Philco Corporation, Philadelphia, Pa., a corporation of Delaware Filed Oct. 22, 1959, Ser. No. 848,008 7 Claims. (Cl. 62278) This invention relates to refrigeration apparatus and, more particularly, is concerned with apparatus of the type having provision for heating the evaporator to defrost the same.

It has been 'known to effect evaporator defrosting by by-passing the refrigerant condenser and flow-restrictor of a refrigerating system and delivering directly to the evaporator hot gaseous refrigerant flowing from the compressor. Such arrangements are intended to result in condensation of the gaseous refrigerant within the evaporator, with resultant heating and consequent defrosting of the latter. Difiiculties arise, however, in practice due to the fact that motor-compressor apparatus ordinarily capable of handling loads imposed under refrigerating conditions tend to become overloaded under hot-gas defrosting conditions to such an extent that the protective relay means, which is normally provided, terminates operation of the motor-compressor before defrosting of the evaporator is completed.

It is well recognized, in the field of two-temperature refrigerators, that evaporators for cooling high temperature food storage compartments require defrosting at relatively frequent intervals, for example upon each refrigerating cycle of the motor-compressor, while evaporators for cooling low temperature compartments normally need be defrosted at less frequent intervals.

The above-indicated problem of motor-compressor overloading has been met by provision of motor-compressors equipped with higher torque motors which have been correspondingly less economical. However, the need for effecting hot-gas defrost of a low temperature evaporator is relatively infrequent, and higher torque capacity motorcompressors, which are expensive as respects both equipment and operational costs, are not required during normal refrigerating operation.

With the foregoing in mind it is a broad objective of the invention to provide improved means for effecting hot-gas defrosting of evaporator means.

It is a specific objective of the invention to provide a hot-gas defrosting system which not only is highly effec tive in producing adequate defrosting, but which system also is extremely simple, inexpensive, and adapted for use with 'a relatively low torque capacity motor-compressor.

In achievement of the foregoing objectives, the invention comprises, in novel combination with a bypass conduit or connection serving to deliver hot gaseous refrigerant to evaporator means, an accumulator or sump means disposed within the system between the refrigerant fiow restrictor and the evaporator means .and serving, under normal refrigerating conditions, to accommodate flow of refrigerant between the restrictor and evaporator means. In particular accordance with the invention, bypassed gaseous refrigerant is delivered to the evaporator means, during defrosting of the same, while liquid refrigerant is caused to become entrapped in-the sump means thereby effectively reducing the amount of refrigerant pumped by the motor-compressor during the defrost period, with a resultant advantageous reduction of load on the same.

The objects and features of the invention, together with significant details of construction thereof, will be understood from a consideration of the following description taken in conjunction with the accompanying drawing, in which:

FIGURE 1 is a diagrammatic representation of a refrigeration system disposed within a cabinet, and including defrosting apparatus embodying the present invention; and

FIGURE 2 is a somewhat enlarged sectional showing,

with parts broken away of apparatus seen in FIGURE 1.

Now making detailed reference to the drawing, it will be seen that the illustrated embodiment of the invention includes the elements of a refrigeration system of conventional dual-evaporator type, said system having a motor-compressor 10, a condenser 11, a continuously open restricted connection or capillary tube 12, a first evaporator 14 disposed in heat exchange relation with a freezing compartment 15 to be cooled, and a second evaporator 16 disposed in heat exchange relation with a food compartment 17 to be cooled, each said compartment being disposed in cabinet structure 13 diagrammatically represented by broken lines. The aforesaid elements are connected in series flow circuit through the agency of suitable conduits and connections including the aforesaid capillary tube 12 and a suction line 21. The capillary tube 12 and the suction line 21 are disposed in heat exchange relation with one another, as seen at 20, not only in accordance with usual practice to optimize the refrigeration effect during the refrigeration cycle, but also, as will be hereinafter more fully understood, to function in a novel and advantageous manner during the defrosting cycle. In accordance with usual practice, an accumulator 22 is disposed in the circuit between the outlet of second evaporator 16 and suction line 21.

As seen also in FIGURE 2, and in particular accordance with this invention, sump means 23, generally U- shaped and including vertically extending interconnected leg portions 23a and 23b, is disposed within compartment 15 and interconnects the outlet of capillary tube 12 with the inlet of evaporator 14. Portion 23a is of considerably larger diameter than portion 23b and comprises the major volume of the sump means, leg portions of the sump means being of substantially the same height.

A by-pass connection or conduit 24 extends between the inlet of condenser 11 and the juncture of sump means 23 with the inlet to freezer evaporator 14. By-pass conduit 24 is preferably controlled by a solenoid actuated valve 25.

During normal operation of the system, as indicated by the solid line flow arrows, refrigerant is caused by motor-compressor 10 to fiow from condenser 11 through capillary tube 12, then through sump means 23 and into first evaporator 14. From first evaporator 14 refrigerant flows into the second evaporator 16, through accumulator 22 and returns to motor-compressor 10 by way of suction line 21. The system, during normal operation, includes thermostatic control means 26 adapted to control energization of motor-compressor 10 to provide for onf and off periods thereof in accordance with predetermined desired temperature levels within food compartment 17 and freezer compartment 15.

In accordance with usual practice, thermostatic control means 26 is operative to effect actuation of the motorcompressor to provide above and below freezing temperatures of evaporator 16 and thereby to defrost the same upon each motor-compressor deenergization period.

Freezer evaporator 14, on the other hand, remains at a substantially fixed below-freezing temperature during the refrigerating cycle and is therefore not defrosted along with evaporator 16. Furthermore, freezer compartment 15 normally is opened less often than food compartment 17, with a resultant lesser tendency of freezer evaporator 14 to accumulate frost, in comparison with the degree of frost accumulation by food compartment evaporator 16.

Preferably, although not necessarily, thermostatic means 26 comprises a switch 27 responsive to the pressure of a vaporizable fluid contained within feeler bulb 31 disposed generally in heat exchange relation with evaporator 16. As will be understood, without detailed description, closing of switch 27 places the motor-compressor across the line L to effect normal operation of the motor-compressor and of the system. -Note that during this normal opera tion, sump means 23 merely serves as a refrigerant feeder tube for freezer evaporator 14 and the remainder of the circuit.

The control circuit of the illustrated embodiment includes a single throw, double pole switch 32 and the defrosting cycle for removing frost from freezer evaporator 14 is initiated in response to closure of this switch, regardless of the position of the contacts of the thermostatically operated switch 27. As will be understood, the switch 32 shown diagrammatically is indicative of the fact that the invention contemplates inclusion of such apparatus as may be required to initiate and terminate the defrosting cycle. Preferably, although not necessarily switch 32 may be actuated automatically by a variety of different means, a

number of which are known in the art.

The aforesaid closing of switch 32 places the solenoid of valve 25 across the line L thereby opening the valve and concurrently energizing the motor-compressor. It will be noted that the circuit arrangement is such that energization of the motor-compressor is accomplished even in the event that the contacts of thermostatic switch 27 should be open when defrosting is initiated.

When modified flow of refrigerant has been established within the system, by opening valve 25, hot gaseous refrigerant flows, as indicated by the broken line arrows, first to evaporators 14 and 16, by-passing condenser 11 and restrictor 12. Liquid refrigerant within evaporators 14 and 16 and accumulator 22 is replaced by hot gaseous refrigerant flowing through by-pass conduit 24, such gaseous refrigerant being at an elevated temperature and giving up its heat to the relatively cold evaporators 14 and 16, with the result that some condensation occurs within the evaporators. This condensation of gaseous refrigerant takes place at a temperature, and corresponding pressure, just above 32 F., since the temperature cannot rise materially above this value until all of the frost has been melted from the evaporators, and particularly from freezer evaporator 14. It will be understood that defrosting is accomplished by the aforesaid heat transfer which effects the condensation taking place within the evaporators.

Upon more detailed consideration of operation of the apparatus during defrosting it will be appreciated that opening of by-pass valve 25 reduces the pressure drop normally provided by capillary tube 12 between the motorcompressor and the evaporators, and the relatively high pressure refrigerant within condenser 11 and capillary tube 12 flows through by-pass line 24 into relatively low pressure evaporators 14 and 16 until such time as the pressure differential becomes insuflicient to effect such flow.

As defrosting continues, hot gaseous refrigerant flowing through by-pass 24 is forced at considerable velocity through evaporators 14, 16 and accumulator 22 to flush liquid refrigerant therefrom into the suction line 21. The resultant flow of refrigerant through line 21 is characterized by the presence of relatively cold liquid refrigerant interspersed by pockets of gaseous refrigerant. This relatively cold liquid refrigerant flowing through the suction line absorbs heat from refrigerant in capillary tube 12, in the region of the heat exchange 20 between tube 12 and line 21, in an amount sufficient to effect condensation of any gaseous refrigerant within the capillary tube and some evaporation of liquid refrigerant in the suction line prior to its entry into the motor-comprsesor, the heat and low pressure of the latter effecting re-evaporation of any liquid refrigerant prior to its being forced through by-pass line 24 in continuation of the defrosting cycle.

Liquid refrigerant in the capillary tube is caused by the motor-compressor to-flow into sump means 23 to become entrapped therein, as seen in FIGURE 2. Inasmuch as sump means 23 is relatively cold, for example, by virtue of being disposed within compartment 15, any gaseous refrigerant flowing from the capillary tube 12 or from by-pass line 24 at this time into the sump means will condense and also become entrapped therein. The columns of liquid in each of leg portions 23a and 23b substantially balance one another under these conditions, and in the absence of sufficient gas pressure differential on the surfaces of the liquid in the sump means at this time no flow of iiquid therefrom will take place. Entrapment of liquid refrigerant in the sump means effectively reduces the quantity of refrigerant within the evaporator system during this phase of the defrosting cycle. As defrosting continues, the supply of liquid refrigerant passing from accumulator 22 through suction line 21 is depleted, the refrigerant pumped at this time being in the form of superheated vapor. It is of course the introduction of this superheated vapor into the motor-compressor which effectively reduces the rate of loading of the same, inasmuch as there is a reduction in the amount of vaporizable refrigerant capable of effecting an increase in back pressure at the motor-compressor. This superheated vapor does, however, absorb some heat in the motor-compressor, which heat is given up to the evaporator further to defrost the same. It is well recognized, however, that the amount of heat capable of being absorbed and given up by given quantities of superheated gaseous refrigerant is considerably less than is available by effecting changes of state of like quantities of liquid and gaseous refrigerant. It will, therefore, be seen from whatfollows that the present invention advantageously provides, automatically, an increase in the quantity of gaseous superheated refrigerant being handled by the motor-compressor to increase the heat input to the evaporator system, the pumping of additional superheated gaseous refrigerant effecting but a relatively small increase of load upon the compressor.

As defrosting continues, the superheated gaseous refrigerant within suction line 21 cannot remove heat from capillary tube 12 in an amount sufficient to liquify gaseous refrigerant flowing therethrough into sump means 23. The force of this gaseous refrigerant upon the relatively large surface area of liquid in leg portion 23a is sufficient to effect liquid flow from the sump means into the evaporators. This liquid refrigerant is then substantially completely vaporized 'upon contact with hot gaseous refrigerant flowing from by-pass line 24, through the suction line, and back to the compressor where it absorbs heats and is pumped again to the evaporators to give up heat thereto.

The defrosting period is therefore characterized by a substantially automatic decrease in the defrosting rate, followed by substantial restoration thereof, whereby the net effect is, of course, attenuation of the load on the motor-compressor. in the absence of this novel provision for modulating the load, it would continue to rise, undesirably, to a level resulting in operation of the overload protection means before completion of defrosting.

From the foregoing description it is clear that the present invention provides a hot gas defrosting system which is characterized by unusual constructional simplicity, by a high degree of reliability in operation, and by minimal power requirement at the motor compressor.

I claim:

1. In a refrigeration system having compressor, condenser, restrictor and evaporator elements normally so connected that refrigerant flows through said elements in the order named, whereby to vaporize refrigerant within said evaporator, means for modifying the flow of refrigerant through said'system to cause condensation of refrigerant within the evaporator and consequent heating of the latter, including conduit means by-passing said restrictor and said condenser and operable to deliver to said evaporator hot gaseous refrigerant flowing from the compressor, to effect the aforesaid condensation and nsequent heating of the evaporator, and apparatus adayed effectively to decrease the quantity of liquid refrigerant active in the system under the aforesaid modified con dition of operation said apparatus comprising: means providing high heat exchange relation, under such modified conditions, between refrigerant flowing through the restrictor and refrigerant flowing through the connection between the evaporator and the compressor; and a vessel having an upstanding larger diameter conduit in open communication at an upper end portion thereof with said restrictor, said vessel further having a lesser diameter upstanding conduit disposed in fluid flow communication with the other conduit at a level below the recited upper end portion with which said restrictor is in open communication and connected to said evaporator at a level above the recited region of fluid flow communication between said upstanding conduits and serving, under normal conditions of operation, to provide for flow of liquid refrigerant from said restrictor to said evaporator, the outlet of the lesser diameter conduit of said vessel being disposed in open communication with said by-passconduit means, hot gaseous refrigerant flowing through said condenser and said restrictor during defrosting being caused to be liqu-ified in said restrictor in the region of the said heat exchange means and to flow into said vessel for storage therein during such defrosting.

2. In a refrigeration system of the type having elements including a compressor, a condenser, a restrictor, an evaporator, and conduit means connecting said elements in series flow circuit, means including a valve controlled line by-passing said restrictor and condenser and communicating with said evaporator and being operable to interrupt normal flow of liquid refrigerant to the restrictor and thence to the evaporator to establish modified flow of hot gaseous refrigerant through said line and to said evaporator, means providing high heat exchange relation, under such modified conditions, between refrigerant flowing through the restrictor and refrigerant flowing through the connection between the evaporator and the compressor, and sump means disposed in the circuit between said restrictor and the inlet to said evaporator, said sump means comprising a pair of vertically extending conduit portions disposed in fluid flow communication with one another at their lower ends, one of said conduit portions being substantially larger in cross sectional area than the other of said conduit portions, said restrictor being connected at its outlet to the said conduit portion having the larger area, and said by-pass conduit being connected at its outlet at a location intermediate said evaporator and said sump means conduit portion of lesser cross sectional area, the last recited connections of said restrictor and said bypass conduit being disposed at a level above that of the recited lower ends of the conduit portions that are in fluid flow communication, hot gaseous refrigerant flowing through said condenser and said restrictor during defrosting being caused to be liquified in said restrictor in the region of the heat exchange means and to flow into said sump means for storage therein during such defrosting.

3. In a refrigeration system of the type having elements including a compressor, a condenser, a restrictor, an evaporator, and conduit means connecting said elements in series flow circuit, means including a valve controlled line bypassing said restrictor and condenser and communicating with said evaporator and being operable to interrupt normal flow of liquid refrigerant through the restrictor and thence to the evaporator to establish modified flow of hot gaseous refrigerant through said line and to said evaporator, means providing high heat exchange relation, under such modified conditions, between refrigerant flowing through the restrictor and refrigerant flowing through the connection between the evaporator and the compressor, and sump means disposed in the circuit between said restrictor and the inlet to said evaporator, said sump means comprising a generally Ushaped tube having vertically extending leg portions interconnected by a lower loop portion, one of said leg portions having a larger diameter bore than the other, said restrictor being connected at its outlet to the larger diameter leg portion at a level above said lower loop por tion, and said by-pass conduit being connected at its outlet at a location intermediate said evaporator and said leg portion of lesser diameter, and at a level above said lower loop portion, hot gaseous refrigerant flowing through said condenser and said restrictor during defrosting being caused to be liquified in said restrictor in the region of the said heat exchange means and to flow into said sump means for storage therein during such defrosting.

4. Defrostable refrigeration apparatus comprising, in combination: a compressor; a condenser; a capillary tube restrictor; an evaporator; conduit means including suction and feed lines interconnecting said compressor, condenser; restrictor, and evaporator in series flow circuit in such manner that refrigerant normally flows from the discharge side of said compressor through said condenser and restrictor, to said evaporator, the refrigerant thereafter returning to the suction side of said compressor through said suction line, said suction line being disposed in high heat exchange relation with said capillary tube restrictor; means including a valve controlled line bypassing said restrictor and said condenser and communieating with said evaporator and being operable to interrupt normal flow of liquid refrigerant through the restrictor and thence to the evaporator and to establish modified flow of hot gaseous refrigerant through said line and to said evaporator, whereby to provide for condensing of refrigerant in the latter, the heat exchange relation between said suction line and said restrictor being effective during the flow of hot gaseous refrigerant through the valve controlled line to permit relatively cold liquid refrigerant flowing ifrom said evaporator through said suction line to absorb heat from the gaseous refrigerant flowing through said restrictor and to condense the same prior to its exit therefrom; and tubular sump means disposed in open communication With said conduit means and interconnecting said restrictor and said evaporator, said sump means having a. smaller diameter upstanding conduit portion connected toward its upper end with said evaporator in the region of connection of said valve controlled line, said sump means further having a large diameter upstanding conduit portion in fluid flow communication at its lower end with the lower end of said smaller diameter portion, and dipsosed and adapted to store the relatively small quantity of refrigerant which flows into the upper portion thereof from said condenser through said restrictor during the flow of hot gaseous refrigerant through said valve controlled line.

5. In a refrigeration system having compressor, condenser, restrictor and evaporator elements normally. so connected that refrigerant flows through said elements in the order named, whereby to vaporize refrigerant within said evaporator, means for modifying the flow of refrigerant through said system to cause condensation of refrigerant Within the evaporator and consequent heating of the latter, including conduit means by-passing said restrictor and operable to deliver to said evaporator hot gaseous refrigerant flowing from the compressor, to effeet the aforesaid condensation and consequent heating of the evaporator, and apparatus adapted effectively to decrease the quantity of liquid refrigerant active in the system under the aforesaid modified condition of opera tion, said apparatus comprising: means providing high heat exchange relation, under such modified conditions, between refrigerant flowing through the restrictor and refrigerant flowing through the connection between the evaporator and the compressor; and a vessel having an upstanding large diameter conduit in open communication at an upper end portion thereof with said restrictor, said vessel further having a lesser diameter upstanding conduit disposed in fluid flow communication with the other conduit at a level below the recited upper end portion with which said restrictor is in open communication and connected to said evaporator at a level above the recited region of fluid flow communication between said upstanding conduits and serving, under normal condi- 1 tion of operation, to provide for flow of liquid refrigerant from said restrictor to said evaporator, the outlet of the lesser diameter conduit of said vessel being disposed in open communication with said by-pass conduit means, hot gaseous refrigerant flowing through said restrictor during defrosting being caused to be liquified in the latter in the region of the said heat exchange means and to flow into said vessel for storage therein during defrosting.

6. Defrostable refrigeration apparatus comprising, in combination: compressor means; condenser means; capillary tube restrictor means; evaporator means; conduit means including suction and feed lines interconnecting said compressor, condenser, restrictor and evaporator means in series flow circuit in such manner that refrigerant normally flows from the discharge side of said compressor means through said condenser and restrictor means to said evaporator means, the refrigerant thereafter returning to the suction side of said compressor means through said suction line, said suction line disposed in high heat exchange relation with said capillary tube restrictor means; means including a valve controlled conduit bypassing said restrictor means and communicating with said evaporator means and being operable to interrupt normal flow of liquid refrigerant through the restrictor means and thence to the evaporator means and to establish modified flow of hot gaseous refrigerant through said conduit and to said evaporator means whereby to provide for condensing of refrigerant in the latter; and tubular sump means disposed in open communication with said conduit and interconnecting said restrictor means and said evaporator means, said sump means having a smaller diameter upstanding portion connected toward its upper end with said evaporator in the region of connection of said valve controlled conduit, said sump means further having a larger diameter upstanding portion in fluid flow communication at its lower end with the lower end of said smaller diameter portion and disposed and adapted to store refrigerant which flows into the upper portion thereof from said condenser means through said restrictor means during the flow of hot gaseous refrigerant through the said conduit, the recited heat exchange relation between said capillary tube restrictor means and said suction line being effective during the flow of hot gaseous refrigerant through the said valve controlled conduit to permit the relatively cold liquid refrigerant flowing from said evaporator means through suction line to absorb heat from gaseous refrigerant flowing through said restrictor means to condense the same prior to its entry into said sump means for storage therein.

7. In a refrigeration system having compressor, condenser, restrictor and evaporator elements normally so connected that refrigerant flows through said elements in the order named, whereby to vaporize refrigerant within said evaporator, means for modifying the flow of refrigerant through said system to cause condensation of refrigerant within the evaporator and consequent heating of the latter, including conduit means by-passing said restrictor and operable to deliver to said evaporator hot gaseous refrigerant flowing from the compressor, to effect the aforesaid condensation and consequent heating of the evaporator, and apparatus adapted effectively to decrease the quantity of liquid refrigerant active in the system under the aforesaid modified condition of operation, said apparatus comprising: means providing high heat exchange rela tion under such modified conditions, between refrigerant flowing through the restrictor and refrigerant flowing through the connection between the evaporator and the compressor, and a vessel having an upstanding conduit in open communication at an upper end portion thereof with the restrictor, said vessel further having another upstanding conduit disposed in fluid flow communication with the first recited conduit at a level below the recited upper end portion at which said restrictor is in open communication and connected to said evaporator at a level above the recited region of fluid flow communication between said upstanding conduits and serving, under normal condition of operation, to provide for flow of liquid refrigerant from said restrictor to said evaporator, the outlet of the second recited conduit of said vessel being disposed in open communication with said bypass conduit means, hot gaseous refrigerant flowing through said condenser and said restrictor during defrosting being caused to be liquefied in said restrictor in the region of the said heat exchange means and to flow into said vessel for storage therein during such defrosting.

References Cited in the file of this patent UNITED STATES PATENTS 2,666,298 Jones Ian. 19, 1954 2,666,299 Sutton Jan. 19, 1954 2,718,764 Kramer Sept. 27, 1955 2,720,759 Philipp Oct. 18, 1955 2,783,621 Staebler Mar. 5, 1957 2,857,746 Philipp Oct. 28, 1958 2,957,316 Buchanan Oct. 25, 1960 

2. IN A REFRIGERATION SYSTEM OF THE TYPE HAVING ELEMENTS INCLUDING A COMPRESSOR, A CONDENSER, A RESTRICTOR, AN EVAPORATOR, AND CONDUIT MEANS CONNECTING SAID ELEMENTS IN SERIES FLOW CIRCUIT, MEANS INCLUDING A VALVE CONTROLLED LINE BY-PASSING SAID RESTRICTOR AND CONDENSER AND COMMUNICATING WITH SAID EVAPORATOR AND BEING OPERABLE TO INTERRUPT NORMAL FLOW OF LIQUID REFRIGERANT TO THE RESTRICTOR AND THENCE TO THE EVAPORATOR TO ESTABLISH MODIFIED FLOW OF HOT GASEOUS REFRIGERANT THROUGH SAID LINE AND TO SAID EVAPORATOR, MEANS PROVIDING HIGH HEAT EXCHANGE RELATION, UNDER SUCH MODIFIED CONDITIONS, BETWEEN REFRIGERANT FLOWING THROUGH THE RESTRICTOR AND REFRIGERANT FLOWING THROUGH THE CONNECTION BETWEEN THE EVAPORATOR AND THE COMPRESSOR, AND SUMP MEANS DISPOSED IN THE CIRCUIT BETWEEN SAID RESTRICTOR AND THE INLET TO SAID EVAPORATOR, SAID SUMP MEANS COMPRISING A PAIR OF VERTICALLY EXTENDING CONDUIT PORTIONS DISPOSED IN FLUID FLOW COMMUNICATION WITH ONE ANOTHER AT THEIR LOWER ENDS, ONE OF SAID CONDUIT PORTIONS BEING SUBSTANTIALLY LARGER IN CROSS SECTIONAL AREA THAN THE OTHER OF SAID CONDUIT PORTIONS, SAID RESTRICTOR BEING CONNECTED AT ITS OUTLET TO THE SAID CONDUIT PORTION HAVING THE LARGER AREA, AND SAID BY-PASS CONDUIT BEING CONNECTED AT ITS OUTLET AT A LOCATION INTERMEDIATE SAID EVAPORATOR AND SAID SUMP MEANS CONDUIT PORTION OF LESSER CROSS SECTIONAL AREA, THE LAST RECITED CONNECTIONS OF SAID RESTRICTOR AND SAID BYPASS CONDUIT BEING DISPOSED AT A LEVEL ABOVE THAT OF THE RECITED LOWER ENDS OF THE CONDUIT PORTIONS THAT ARE IN FLUID FLOW COMMUNICATION, HOT GASEOUS REFRIGERANT FLOWING THROUGH SAID CONDENSER AND SAID RESTRICTOR DURING DEFROSTING BEING CAUSED TO BE LIQUIFIED IN SAID RESTRICTOR IN THE REGION OF THE HEAT EXCHANGE MEANS AND TO FLOW INTO SAID SUMP MEANS FOR STORAGE THEREIN DURING SUCH DEFROSTING. 